Jan 14 (Reuters) - New Jersey Governor Chris Christie, facing investigations over a traffic snarl-up and the use of federal money for an ad campaign, will likely try to shift attention back to his second-term agenda when he gives a key speech on Tuesday.

Christie, a charismatic conservative and an early favorite in the upcoming Republican race for the White House in 2016, was re-elected in a landslide victory last November.

A pair of scandals in the first weeks of the year have put him on the defensive.

Two sets of emails last week appeared to show that Christie's aides orchestrated lane closures last September in a stretch of highway leading to the George Washington Bridge, which spans New Jersey and Manhattan, and lied about it.

Christie has denied any knowledge of a scheme to snarl traffic to wreak political payback against the Democratic mayor of the city of Fort Lee, New Jersey, and said there is nothing in the emails to suggest he had any direct knowledge of it.

While Christie is likely to use his State of the State speech to address these challenges, he is also expected to tout his accomplishments and set out priorities for the year.

"These are our achievements: Four balanced budgets. Passed with bipartisan support. Pension reform and tenure reform. Passed with bipartisan support. A cap on property taxes. Passed with bipartisan support," Christie planned to say according to excerpts of his remarks released ahead of delivery. "We acted and we acted together."

Those could include an across-the-board tax cut, an idea he proposed in 2012, which has been delayed as revenue has fallen below expectations, as well as ways to generate more job growth.

The state's economy has seen signs of improvement over the last several months. Its unemployment rate experienced its largest monthly drop on record in November, dropping by 0.6 percentage point to 7.8 percent, according to the state labor department.

Revenue has also been recovering steadily. In the first five months of fiscal 2014, which began on July 1, New Jersey took in 7.9 percent more revenue - from income, sales, corporate and other taxes - than for the same period the year before. But that's still 1.2 percent, or $98 million, under budget.

Still, the state's fiscal situation, and Christie's ideas for improving it, could be overshadowed by his response to the scandals and speculation about his political future.

Since taking office four years ago, Christie - a former federal prosecutor - has built a national reputation as a Republican capable of winning bipartisan support for his conservative priorities, like spending cuts, while repairing New Jersey's reputation for corruption and graft.

A prolific fundraiser for Republicans across the country, Christie has taken on a leadership role with the Republican Governor's Association.

But the brewing scandals threaten to tarnish that reputation and Christie's national appeal.

A Reuters/Ipsos poll showed the bridge closure scandal had taken a toll on Christie's image, with 26 percent of those asked saying they were now less favorable towards him, compared with 3 percent who said they were more favorable and 41 percent, whose view was the same. More respondents believed he had a hand in the scandal, with 31 percent saying they thought he was aware his staff intentionally caused the traffic jam, compared with 28 percent, who said they believed his statements that he was in the dark.

The poll showed Christie was still the leading Republican White House contender, backed by 18 percent of those asked, narrowly leading Congressman Paul Ryan, who was favored by 17 percent of those asked.

The poll was conducted Jan. 10-14 among 1,245 online respondents, with a credibility interval of 3.2 percentage points.

Democrats, who control both houses of the state legislature, have called a special session to address the traffic scandal.

Meanwhile, a New Jersey Democrat has requested a federal probe into the use of storm relief funds for an ad campaign, intended to draw visitors back to the Jersey Shore, that featured Christie as he was seeking re-election. (Additional reporting by Hilary Russ and Zach Cook; Editing by Eric Walsh and Andrew Hay)

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